The present invention relates to an aminostyrylanthracene compound suitable as an organic luminescent material emitting any desired color and a synthetic intermediate thereof, and a process for production thereof.
The organic electroluminescent element (EL element) is recently attracting attention as a candidate for the flat panel display which emits natural light, has a high response speed, and has no dependence on viewing angle. Thus, the organic luminescent material constituting EL elements is arousing acute interest. The first advantage of the organic luminescent material is that its optical properties can be controlled to a certain extent by molecular design. This makes it possible to realize a full-color organic luminescent element made of luminescent materials emitting three primary colors (red, blue, and green) individually.
Styryl compounds represented by the following general formula [A] find use as an organic electroluminescent material and also find use in various applications because they emit intense light (ranging from blue to red in the visible region) depending on the substituent introduced thereinto. In addition, being sublimable, they offer the advantage of forming a uniform amorphous film by vacuum deposition. The present-day molecular orbital calculations permit one to make an approximate prediction of the material""s optical properties. In actual, a technology to produce the desired material efficiently is most important for industry. 
(where, in the general formula [A] above, Ar represents an aryl group which may have a substituent, Ra and Rb each represent a hydrogen atom, a saturated or unsaturated hydrocarbon group, an aryl group which may have a substituent, a cyano group, a halogen atom, a nitro group, a hydrocarbon oxy group, or a hydrocarbon amino group, which may be identical or different.)
Organic luminescent materials produced so far are mostly those compounds represented by the general formula [A] above. Many of them emit light of blue to green, and only a few of them emit light of yellow to red. [The Institute of Electronics, Information and Communication Engineers; Technical Research Report; Organic Electronics, 17, 7 (1992), Inorganic and Organic Electroluminescence 96 Berlin, 101 (1996)] There has been no established method for their efficient production.
It is an object of the present invention, which was completed in view of the present state mentioned above, to provide a compound suitable for use as an organic luminescent material emitting intense yellow to red light, a synthetic intermediate thereof, and a process for its efficient production.
In order to address the above-mentioned problem, the present inventors carried out extensive studies. As the result, they found that an aminostyrylanthracene compound represented by the general formula [I], [II], [III], or [IV] emits intense light and hence is useful as a luminescent material for yellow to red light, and they also established a general, efficient process for its production.
First, the present invention relates to an aminostyrylanthracene compound represented by the following general formula [I], [II], [III], or [IV]. (referred to as xe2x80x9cthe compound of the present inventionxe2x80x9d hereinafter) 
[where, in the general formula [I] above, R2 represents an unsubstituted aryl group, R1 represents an aryl group represented by the following general formula (1), 
(where, in the general formula (1) above, R6, R7, R8, R9, and R10 are identical or different groups, each representing a hydrogen atom, a saturated or unsaturated hydrocarbon oxy group having one or more carbons, a hydrocarbon group, a hydrocarbon amino group, a fluoroalkyl group, or an aryl group which may have a substituent.) R3 and R4 are identical or different groups, at least one of them being a hydrogen atom, a cyano group, a fluoroalkyl group, a nitro group, or a halogen atom, and R5 represents a hydrogen atom, a saturated or unsaturated hydrocarbon group having one or more carbons, or an aryl group which may have a substituent.]
[where, in the general formula [II] above, R11 and R12 are identical or different groups, each representing an aryl group represented by the following general formula (2), 
(where, in the general formula (2) above, R16, R17, R18, R19, and R20 are identical or different groups, each representing a hydrogen atom, a saturated or unsaturated hydrocarbon oxy group having one or more carbons, a hydrocarbon group, a hydrocarbon amino group, a fluoroalkyl group, or an aryl group which may have a substituent.) R13 and R14 are identical or different groups, at least one of them being a hydrogen atom, a cyano group, a fluoroalkyl group, a nitro group, or a halogen atom, and R15 represents a hydrogen atom, a saturated or unsaturated hydrocarbon group having one or more carbons, or an aryl group which may have a substituent.]
[where, in the general formula [III] above, R21 represents an aryl group represented by the following general formula (3), 
(where, in the general formula (3) above, R26, R27, R28, R29, and R30 are identical or different groups, each representing a hydrogen atom, a saturated or unsaturated hydrocarbon oxy group having one or more carbons, a hydrocarbon group, a hydrocarbon amino group, or a fluoroalkyl group.) R22 represents an aryl group represented by the following general formula (4), 
(where, in the general formula (4) above, R31, R32, R33, R34, R35, R36, and R37 are identical or different groups, each representing a hydrogen atom, a saturated or unsaturated hydrocarbon oxy group having one or more carbons, a hydrocarbon group, a hydrocarbon amino group, a fluoroalkyl group, or an aryl group which may have a substituent.) R23 and R24 are identical or different groups, at least one of them being a hydrogen atom, a cyano group, a fluoroalkyl group, a nitro group, or a halogen atom, and R25 represents a hydrogen atom, a saturated or unsaturated hydrocarbon group having one or more carbons, or an aryl group which may have a substituent.]
[where, in the general formula [IV] above, R38 and R39 are identical or different groups, at least one of them being a hydrogen atom or a saturated or unsaturated hydrocarbon group having one or more carbons, R40 and R41 are identical or different groups, each representing a hydrogen atom, a cyano group, a fluoroalkyl group, a nitro group, or a halogen atom, and R42 represents a hydrogen atom, a saturated or unsaturated hydrocarbon group having one or more carbons, or an aryl group which may have a substituent.]
The compound of the present invention can be effectively used as an organic luminescent material which emits yellow to red light. It has a high glass transition point and a high melting point. It is stable electrically, thermally, and chemically and is amorphous. It easily takes on a glassy state and hence is capable of vapor deposition.
The compound of the present invention should preferably be one which is represented by any of the following general formulas. 
[where, in the general formula (5) above, Ar1 and Ar2 are identical or different aryl groups which may have a substituent and, if they have a substituent, they represent a group selected from aryl groups represented by the following general formulas (6), (7), (8), (9), (10), and (11). 
(where, in the general formulas (6), (7), (8), (9), (10), and (11) above, R44, R45, and R46 each represent a saturated or unsaturated hydrocarbon group having one or more carbons (preferably 1 to 6) or a fluoroalkyl group, R47, R48, R49, R50, R51, and R52 are identical or different groups, each representing a saturated or unsaturated hydrocarbon group having one or more carbons (preferably 1 to 6 carbons), or a fluoroalkyl group, n is an integer of 0 to 5, m is an integer of 0 to 3, and 1 is an integer of 0 to 3), R43 represents a hydrogen atom, a saturated or unsaturated hydrocarbon group having one or more carbons, or an aryl group which may have a substituent.]
To be more concrete, the compound of the present invention should preferably be one which is represented by the following general formula (12), (13), (14), (15), (16), (17), or (18). 
(where, in the general formula (12) above, R53 represents a saturated or unsaturated hydrocarbon group having 1 to 6 carbons or an aryl group which may have a substituent, and R54 represents a hydrogen atom, a saturated or unsaturated hydrocarbon group having 1 to 6 carbons, or an aryl group which may have a substituent.) 
(where, in the general formula (13) above, R55 represents a saturated or unsaturated hydrocarbon group having 1 to 6 carbons, a trifluoromethyl group, or an aryl group which may have a substituent, and R56 represents a hydrogen atom, a saturated or unsaturated hydrocarbon group having 1 to 6 carbons, or an aryl group which may have a substituent.) 
(where, in the general formula (14) above, R57 and R58 each represent a saturated or unsaturated hydrocarbon group having 1 to 6 carbons, a trifluoromethyl group, or an aryl group which may have a substituent, and R59 represents a hydrogen atom, a saturated or unsaturated hydrocarbon group having 1 to 6 carbons, or an aryl group which may have a substituent.) 
(where, in the general formula (15) above, R60 represents a saturated or unsaturated hydrocarbon group having 1 to 6 carbons or an aryl group which may have a substituent, and R61 represents a hydrogen atom, a saturated or unsaturated hydrocarbon group having 1 to 6 carbons, or an aryl group which may have a substituent.) 
(where, in the general formula (16) above, R62 represents a saturated or unsaturated hydrocarbon group having 1 to 6 carbons or an aryl group which may have a substituent, and R63 represents a hydrogen atom, a saturated or unsaturated hydrocarbon group having 1 to 6 carbons, or an aryl group which may have a substituent.) 
(where, in the general formula (17) above, R64 represents a saturated or unsaturated hydrocarbon group having 1 to 6 carbons or an aryl group which may have a substituent, and R65 represents a hydrogen atom, a saturated or unsaturated hydrocarbon group having 1 to 6 carbons, or an aryl group which may have a substituent.) 
(where, in the general formula (18) above, R66 and R67 each represent a saturated or unsaturated hydrocarbon group having 1 to 6 carbons or an aryl group which may have a substituent, and R68 represents a hydrogen atom, a saturated or unsaturated hydrocarbon group having 1 to 6 carbons, or an aryl group which may have a substituent.)
The compound of the present invention is exemplified by the one which is represented by the following structural formula (19)-1, (19)-2, (19)-3, (19)-4, (19)-5, (19)-6, (19)-7, (19)-8, (19)-9, (19)-10, (19)-11, or (19)-12. 
The compound of the present invention should preferably be one which is represented by the following general formula. 
(where, in the general formula (20) above, Ar1 and Ar2 are identical or different aryl groups which may have a substituent and, if they have a substituent, they represent a group selected from aryl groups represented by the following general formulas (6), (7), (8), (9), (10), and (11). 
(where, in the general formulas (6), (7), (8), (9), (10), and (11) above, R44, R45, R45, and R46 each represent a saturated or unsaturated hydrocarbon group having one or more carbons (preferably 1 to 6 carbons) or a fluoroalkyl group, R47, R48, R49, R50, R51, and R52 are identical or different groups, each representing a saturated or unsaturated hydrocarbon group having one or more carbons (preferably 1 to 6 carbons), or a fluoroalkyl group, n is an integer of 0 to 5, m is an integer of 0 to 3, and 1 is an integer of 0 to 3), and R69 represents a hydrogen atom, a saturated or unsaturated hydrocarbon group or an aryl group which may have a substituent.]
To be more concrete, the compound of the present invention should preferably be one which is represented by the following general formula (21), (22), (23), (24), (25), (26), or (27). 
(where, in the general formula (21) above, R70 represents a saturated or unsaturated hydrocarbon group having 1 to 6 carbons or an aryl group which may have a substituent, and R71 represents a hydrogen atom, a saturated or unsaturated hydrocarbon group having 1 to 6 carbons, or an aryl group which may have a substituent.) 
(where, in the general formula (22) above, R72 represents a saturated or unsaturated hydrocarbon group having 1 to 6 carbons, a trifluoromethyl group, or an aryl group which may have a substituent, and R73 represents a hydrogen atom, a saturated or unsaturated hydrocarbon group having 1 to 6 carbons, or an aryl group which may have a substituent.) 
(where, in the general formula (23) above, R74 and R75 each represent a saturated or unsaturated hydrocarbon group having 1 to 6 carbons, a trifluoromethyl group, or an aryl group which may have a substituent, and R76 represents a hydrogen atom, a saturated or unsaturated hydrocarbon group having 1 to 6 carbons, or an aryl group which may have a substituent.) 
(where, in the general formula (24) above, R77 represents a saturated or unsaturated hydrocarbon group having 1 to 6 carbons or an aryl group which may have a substituent, and R78 represents a hydrogen atom, a saturated or unsaturated hydrocarbon group having 1 to 6 carbons, or an aryl group which may have a substituent.) 
(where, in the general formula (25) above, R79 represents a saturated or unsaturated hydrocarbon group having 1 to 6 carbons or an aryl group which may have a substituent, and R80 represents a hydrogen atom, a saturated or unsaturated hydrocarbon group having 1 to 6 carbons, or an aryl group which may have a substituent.) 
(where, in the general formula (26) above, R81 represents a saturated or unsaturated hydrocarbon group having 1 to 6 carbons or an aryl group which may have a substituent, and R82 represents a hydrogen atom, a saturated or unsaturated hydrocarbon group having 1 to 6 carbons, or an aryl group which may have a substituent.) 
(where, in the general formula (27) above, R82 and R83 each represent a saturated or unsaturated hydrocarbon group having 1 to 6 carbons or an aryl group which may have a substituent, and R85 represents a hydrogen atom, a saturated or unsaturated hydrocarbon group having 1 to 6 carbons, or an aryl group which may have a substituent.)
The compound of the present invention is exemplified by the one which is represented by the following structural formula (28)-1, (28)-2, (28)-3, (28)-4, (28)-5, (28)-6, (28)-7, (28)-8, (28)-9, (28)-10, (28)-11, or (28)-12. 
The compound of the present invention should preferably be one which is represented by the following general formula. 
(where, in the general formula (29) above, Ar1 and Ar2 are identical or different aryl groups which may have a substituent and, if they have a substituent, they represent a group selected from aryl groups represented by the following general formulas (6), (7), (8), (9), (10), and (11). 
(where, in the general formulas (6), (7), (8), (9), (10), and (11) above, R44, R45, and R46 each represent a saturated or unsaturated hydrocarbon group having one or more carbons (preferably 1 to 6 carbons) or a fluoroalkyl group, R47, R48, R49, R50, R51, and R52 are identical or different groups, each representing a saturated or unsaturated hydrocarbon group having one or more carbons (preferably 1 to 6 carbons), or a fluoroalkyl group, n is an integer of 0 to 5, m is an integer of 0 to 3, and 1 is an integer of 0 to 3), R86 represents a hydrogen atom, a saturated or unsaturated hydrocarbon group having one or more carbons, or an aryl group which may have a substituent.)
To be more concrete, the compound of the present invention should preferably be one which is represented by the following formula (30), (31), (32), (33), (34), (35), or (36). 
(where, in the general formula (30) above, R87 represents a saturated or unsaturated hydrocarbon group having 1 to 6 carbons or an aryl group which may have a substituent, and R88 represents a hydrogen atom, a saturated or unsaturated hydrocarbon group having 1 to 6 carbons, or an aryl group which may have a substituent.) 
(where, in the general formula (31) above, R89 represents a saturated or unsaturated hydrocarbon group having 1 to 6 carbons, a trifluoromethyl group, or an aryl group which may have a substituent, and R90 represents a hydrogen atom, a saturated or unsaturated hydrocarbon group having 1 to 6 carbons, or an aryl group which may have a substituent.) 
(where, in the general formula (32) above, R91 and R92 each represent a saturated or unsaturated hydrocarbon group having 1 to 6 carbons, a trifluoromethyl group, or an aryl group which may have a substituent, and R93 represents a hydrogen atom, a saturated or unsaturated hydrocarbon group having 1 to 6 carbons, or an aryl group which may have a substituent.) 
(where, in the general formula (33) above, R94 represents a saturated or unsaturated hydrocarbon group having 1 to 6 carbons or an aryl group which may have a substituent, and R95 represents a hydrogen atom, a saturated or unsaturated hydrocarbon group having 1 to 6 carbons, or an aryl group which may have a substituent.) 
(where, in the general formula (34) above, R96 represents a saturated or unsaturated hydrocarbon group having 1 to 6 carbons or an aryl group which may have a substituent, and R97 represents a hydrogen atom, a saturated or unsaturated hydrocarbon group having 1 to 6 carbons, or an aryl group which may have a substituent.) 
(where, in the general formula (35) above, R98 represents a saturated or unsaturated hydrocarbon group having 1 to 6 carbons or an aryl group which may have a substituent, and R99 represents a hydrogen atom, a saturated or unsaturated hydrocarbon group having 1 to 6 carbons, or an aryl group which may have a substituent.) 
(where, in the general formula (36) above, R100 and R101 each represent a saturated or unsaturated hydrocarbon group having 1 to 6 carbons or an aryl group which may have a substituent, and R102 represents a hydrogen atom, a saturated or unsaturated hydrocarbon group having 1 to 6 carbons, or an aryl group which may have a substituent.)
To be concrete, the compound of the present invention is exemplified by the one which is represented by the following structural formula (37)-1, (37)-2, (37)-3, (37)-4, (37)-5, (37)-6, (37)-7, (37)-8, (37)-9, (37)-10, (37)-11, or (37)-12. 
The compound of the present invention may be exemplified by the following compounds in addition to those mentioned above. (There are some duplicates.) 
According to the present invention, the compound of the present invention is produced efficiently by a process which comprises condensing an aminobenzaldehyde represented by the following general formula [V] with a phosphonic ester represented by the following general formula [VI] or a phosphonium salt represented by the following general formula [VII], thereby giving an aminostyrylanthracene compound represented by the general formula [I], [II], [III], or [IV] above. 
(where, in the general formula [V] above, R103 and R104 each represent the group corresponding to R1, R2, R11, R12, R21, R22, R38, or R39 mentioned above.) 
(where, in the general formulas [VI] and [VII] above, R105 represents a hydrocarbon group (preferably a saturated hydrocarbon group having 1 to 4 carbons), R106 and R107 each represent the group corresponding to R3, R4, R13, R14, R23, R24, R40, or R41 mentioned above, R108 represents the group corresponding to the R5, R16, R25, or R42 mentioned above, and X represents a halogen atom.)
To be concrete, the process for producing the compound of the present invention comprises performing said condensation by Wittig-Horner reaction or Wittig reaction, treating said phosphonic ester and/or said phosphonium salt with a base in a solvent, thereby giving carboanions, and condensing these carboanions with said aminobenzaldehyde.
The aminostyrylanthracene compound represented by the following general formula (5) 
[where, in the general formula (5) above, Ar1, Ar2 and R43 are defined as above.] is obtained by condensing 4-(N,N-diarylamino)benzaldehyde represented by the following general formula (38) with a phosphonic ester represented by the following general formula (39) or a phosphonium salt represented by the following general formula (40). 
(where, in the general formulas (38), (39), and (40) above, Ar1, Ar2, R105, and X are defined as above.)
The reaction may be expressed by the reaction scheme 1 as follows. 
This reaction starts with treatment of the compound represented by the general formula (39) or (40) with a base in an appropriate solvent. This treatment evolves carboanions, which are subsequently condensed with an aldehyde represented by the general formula (38) so that the reaction is completed. Possible base/solvent combinations are as follows.
Sodium hydroxide/water, sodium carbonate/water, potassium carbonate/water, sodium ethoxide/ethanol or dimethylformamide, sodium methoxide/methanol-diethyl ether mixture or dimethylformamide, triethylamine/ethanol or diglyme or chloroform or nitromethane, pyridine/methylene chloride or nitromethane, 1,5-disazabicyclo[4.3.0]non-5-en/dimethylsulfoxide, potassium t-butoxide/dimethylsulfoxide or tetrahydrofuran or benzene or dimethylformamide, phenyl lithium/diethyl ether or tetrahydrofuran, t-butyl lithium/diethyl ether or tetrahydrofuran, sodium amide/ammonia, sodium hydride/dimethylformamide or tetrahydrofuran, triethyl sodium/diethyl ether or tetrahydrofuran, and the like.
This reaction proceeds selectively at a comparative low temperature (xe2x88x9230xc2x0 C. to 30xc2x0 C.). Therefore, the desired product can be purified easily by chromatography. Moreover, the compound of the present invention represented by the general formula (5) is highly crystalline and hence can be purified by recrystallization. The method of recrystallization is not specifically restricted. It may be readily accomplished by dissolving in acetone and adding hexane, or by dissolving in toluene with heating and then concentrating and cooling. This reaction may be carried out at normal pressure for 3 to 24 hours.
The process for producing the compound of the present invention gives an aminostyrylanthracene compound represented by the above-mentioned general formula (12), (13), (14), (15), (16), (17), (18), (21), (22), (23), (24), (25), (26), (27), (30), (31), (32), (33), (34), (35), or (36). To be concrete, the process gives an aminostyrylanthracene compound represented by the above-mentioned general formula (19)-1, (19)-2, (19)-3, (19)-4, (19)-5, (19)-6, (19)-7, (19)-8, (19)-9, (19)-10, (19)-11, (19)-12, (28)-1, (28)-2, (28)-3, (28)-4, (28)-5, (28)-6, (28)-7, (28)-8, (28)-9, (28)-10, (28)-11, (28)-12, (37)-1, (37)-2, (37)-3, (37)-4, (37)-5, (37)-6, (37)-7, (37)-8, (37)-9, (37)-10, (37)-11, or (37)-12.
The present invention also provides a variety of compounds suitable as synthetic intermediates for the compound of the present invention.
The synthetic intermediate compound for the aminostyrylanthracene compound represented by the above-mentioned general formula [I], [II], [III], or [IV] is a phosphonic ester represented by the above-mentioned general formula [VI] or a phosphonium salt represented by the above-mentioned general formula [VII].
This synthetic intermediate (referred to as xe2x80x9cthe synthetic intermediate 1 of the present inventionxe2x80x9d hereinafter) is typically represented by the following general formula (39), (40), (41), (42), (43), or (44). 
The synthetic intermediate of the present invention may be derived from a synthetic intermediate as its precursor in the following manner.
Reaction between a halogenated aryl compound represented by the following general formula [VIII] and a trialkyl phosphite represented by the following general formula [IX] or triphenylphosphine (PPh3) gives a phosphonic ester represented by the above-mentioned general formula [VI] or a phosphonium salt represented by the above-mentioned general formula [VII]. This reaction may be carried out without solvent or in a solvent (such as xylene) having a boiling point higher than 120xc2x0 C. or in a large excess of trialkyl phosphite, at 120-160xc2x0 C. under normal pressure for 0.5 to 24 hours. 
(where, in the general formula [VIII] above, R106 and R107 are identical or different groups, at least one of them representing a hydrogen atom, cyano group, fluoroalkyl group, nitro group, or halogen atom, R108 represents a hydrogen atom, a saturated or unsaturated hydrocarbon group having one or more carbons (preferably 1 to 6 carbons), or an aryl group which may have a substituent, and X represents a halogen atom.)
P(OR105)3xe2x80x83xe2x80x83General formula [IX]
(where, in the general formula [IX] above, R105 represents a hydrocarbon group, particularly a saturated hydrocarbon group having 1 to 4 carbons.)
The present invention also provides a halogenated aryl compound (referred to as xe2x80x9cthe synthetic intermediate 2 of the present inventionxe2x80x9d hereinafter) represented by the above-mentioned general formula [VIII], which is used as a synthetic intermediate to obtain the synthetic intermediate 1.
The synthetic intermediate 2 of the present invention can be obtained by reaction under illumination between an anthracene compound represented by the following general formula [X] and an N-halogenated succinimide represented by the following general formula [XI]. This reaction may be carried out in a solvent (such as carbon tetrachloride, chloroform, benzene, and chlorobenzene) under illumination from a light source (such as high-pressure mercury lamp, low-pressure mercury lamp, xenone lamp, halogen lamp, sunlight, and fluorescent lamp) at 20-120xc2x0 C. under normal pressure for 30-48 hours. 
(where, in the general formula [X] above, R106 and R107 are identical or different groups, at least one of them representing a hydrogen atom, cyano group, fluoroalkyl group, nitro group, or halogen atom, and R108 represents a hydrogen atom, a saturated or unsaturated hydrocarbon group having one or more carbons (preferably 1 to 6 carbons), or an aryl group which may have a substituent.) 
(where, in the general formula [XI] above, X represents a halogen atom.)
The reactions to give the above-mentioned synthetic intermediates 1 and 2 may be expressed by the reaction scheme 2 as follows. 
The compound of the present invention is used as an organic luminescent material for the organic electroluminescent element (EL element) illustrated in FIGS. 10 to 13.
FIG. 10 shows a transmission-type organic electroluminescent element A which is designed such that the emitted light 20 passes through the cathode 3 and hence the emitted light 20 is visible from the side of the protective layer 4. FIG. 11 shows a reflection-type organic electroluminescent element B which is designed such that the emitted light 20 is reflected by the cathode 3.
In FIGS. 10 and 11, there is shown a substrate 1 on which is formed the organic electroluminescent element. The substrate may be formed from glass, plastics, or any other appropriated material. In the case where the organic electroluminescent element is used in combination with any other display element, the substrate may be used in common. There is shown a transparent electrode (anode) 2, which may be ITO (indium in oxide) or SnO2.
There is shown an organic luminescent layer 5, which contains the compound of the present invention as a luminescent material. The luminescent layer may have any known layer construction. In the case where either of the hole transfer layer or the electron transfer layer is formed from a luminescent material, the luminescent layer may be formed from these layers placed one over another, as explained later. Both or either of the hole transfer layer and the electron transfer layer may be of laminate structure composed of thin films of a plurality of materials or may be a thin film composed of a plurality of materials. This structure may be used to increase the charge transfer performance to such an extent as to meet the object of the present invention. Another layer structure that can be used to increase the luminescent performance includes one in which a thin film of at least one kind of fluorescent material is interposed between the hole transfer layer and the electron transfer layer, or one in which at least one kind of fluorescent material is contained in both the hole transfer layer and the electron transfer layer. In this case the layer structure may contain an additional thin film to control the hole transfer or electron transfer, thereby improving the luminescence efficiency.
The compound of the present invention is capable of both electron transfer and hole transfer; therefore, it can be used as the light-emitting layer which functions also as the electron transfer layer or as the light-emitting layer which functions also as the hole transfer layer. The electroluminescent element may be constructed such that the light-emitting layer (which is formed from the compound of the present invention) is interposed between the electron transfer layer and the hole transfer layer.
Incidentally, there is shown a cathode 3 in FIGS. 10 and 11. The cathode may be formed from an alloy of active metal (such as Li, Mg, and Ca) and metal (such as Ag, Al, and In), or may be formed from layers of these metals. In the case of an organic electroluminescent element of transmission type, the cathode may have an adequate thickness so that a desired light transmittance is attained for specific uses. In addition, there is shown a sealing/protective layer 4, which entirely covers the organic electroluminescent element to ensure its performance. It can be formed from any material which maintains air tightness. There is shown a power source 8 to supply electric current.
The organic electroluminescent element according to the present invention may have an organic layer of laminated structure (or single-hetero structure) which is composed of a hole transfer layer and an electron transfer layer. In this case, the hole transfer layer or the electron transfer layer may be formed from the compound of the present invention. Alternatively, the organic layer may be of double-hetero structure, in which a hole transfer layer, a light-emitting layer, and an electron transfer layer are sequentially laminated on top of the other. In this case, the light-emitting layer is formed from the compound of the present invention.
An example of the organic electroluminescent element of layer structure as mentioned above is illustrated in FIG. 3. It consists of a transparent substrate 1, a transparent anode 2, an organic layer 5a (composed of a hole transfer layer 6 and an electron transfer layer 7), and a cathode 3, which are sequentially placed on top of the other. The entire laminate structure is sealed with a protective film 4, which is Organic electroluminescent element C of single-hetero structure.
The element of layer structure shown in FIG. 12 (in which the light-emitting layer is omitted) emits light 20 of desired wavelength from the interface between the hole transfer layer 6 and the electron transfer layer 7. The emitted light is visible through the substrate 1.
An example of laminate structure shown in FIG. 13 consists of a transparent substrate 1, a transparent anode 2, an organic layer 5b (composed of a hole transfer layer 10, a light-emitting layer 11, and an electron transfer layer 12), and a cathode 3, which are sequentially placed on top of the other. The entire laminate structure is sealed with a protective film 4, which is Organic electroluminescent element D of double-hetero structure.
The organic electroluminescent element shown in FIG. 13 works as follows. A dc voltage applied across the anode 2 and the cathode 3 causes holes (injected from the anode 2) to reach the light-emitting layer 11 through the hole transfer layer 10 and also causes electrons (injected from the cathode 3) to reach the light-emitting layer 11 through the electron transfer layer 12. As the result, recombination of electrons and holes takes place in the light-emitting layer 11, thereby giving rise to singlet excitons which emit light of desired wavelength.
In the above-mentioned organic electroluminescent elements C and D, the substrate 1 may be formed from any transparent material such as glass and plastics. If this element is used in combination with other display element or if the elements of laminate structure as shown in FIGS. 12 and 13 are arranged in a matrix, one substrate may be used in common. Also, the elements C and D may be either of transmission type or of reflection type.
The anode 2 is a transparent electrode, which may be made of ITO (indium tin oxide) or SnO2. A thin film of organic substance or organometallic compound may be interposed between the anode 2 and the hole transfer layer 6 (or 10) for improvement in the charge injection efficiency. In the case where the protective film 4 is made of an electrically conductive material such as metal, then the anode 2 may be surrounded by an insulating film.
In the organic electroluminescent element C, the organic layer 5a is composed of the hole transfer layer 6 and the electron transfer layer 7, and the compound of the present invention is contained in either of them. In this case, the hole transfer layer 6 or the electron transfer layer 7 emits light. In the organic electroluminescent element D, the organic layer 5b is composed of the hole transfer layer 10, the light-emitting layer 11 (containing the compound of the present invention), and the electron transfer layer 12 which are laminated on top of the other. The layer structure may be modified in some other ways. For example, either or both of the hole transfer layer and the electron transfer layer may have the light-emitting function.
In a preferred embodiment, the hole transfer layer 6 or the electron transfer layer 7 or the light-emitting layer 11 should be made of the compound of the present invention by vapor deposition. In this case, the compound of the present invention may be used alone or in combination with another hole or electron transfer material (such as aromatic amine and pyrazoline). In addition, the hole transfer layer may be constructed of laminate of several kinds of hole transfer materials for improvement in the hole transfer performance.
In the organic electroluminescent element C, the light-emitting layer may be the electron transferring light-emitting layer 7. In this case, light is emitted from the hole transfer layer 6 or the interface thereof depending on voltage applied from the power source 8. Likewise, in the organic electroluminescent element D, the electron transfer layer 12 or the hole transfer layer 10 may also function as the light-emitting layer 11. A desirable structure for improved light-emitting performance is such that a light-emitting layer 11 containing at least one kind of fluorescent material is interposed between the hole transfer layer 11 and the electron transfer layer 12. Alternatively, the fluorescent material may be contained in either or both of the hole transfer layer and the electron transfer layer. In this case, the layer structure may contain a thin film (such as hole blocking layer and exciton generating layer) to control the transfer of holes or electrons for improvement in the light-emitting performance.
The cathode 3 may be formed from an alloy of active metal (such as Li, Mg, and Ca) and metal (such as Ag, Al, and In). These metals may be used in the form of laminated layers. The thickness and material of the cathode should be properly selected according to the use of the organic electroluminescent element.
The protective film 4 functions as a sealing film. It should cover the organic electroluminescent element entirely so as to improve the charge injection efficiency and the light-emitting efficiency. It may be formed from any material (such as aluminum, gold, and chromium in the form of metal or alloy) so long as it keeps air tightness.
The above-mentioned organic electroluminescent elements works upon application of direct current. However, it may be operated by pulse current or alternating current. The magnitude of current and voltage is not specifically restricted so long as the element is not broken. It is desirable that the element emit light efficiency with a small amount of electric energy in view of the power consumption and life of the organic electroluminescent elements.
The organic electroluminescent elements of the present invention maybe used to construct a flat display as shown in FIG. 14. For full-color display, the organic layer 5 (5a, 5b), each capable of emitting primary color of red (R), green (G), and blue (B), are interposed between the cathode 3 and the anode 2. The cathode 3 and anode 2 may be stripes intersecting each other. Each element is selected by the luminance signal circuit 14 and the control circuit 15 having a shift register. A signal voltage is applied according to the selection, so that the organic layer (pixel) at the intersection of the selected cathode 3 and anode 2 emits light.
An example of passive matrix (8xc3x973 RGB) is shown in FIG. 14. It is constructed such that a laminate 5 is interposed between the cathode 3 and the anode 2. This laminate is composed of the hole transfer layer and at least either of the light-emitting layer and the electron transfer layer. (See FIGS. 12 and 13.) Both the cathode and the anode are patterned in stripe form so that they intersect each other at right angles. Signal voltage is applied sequentially by the control circuits 14 and 15 (with a shift register). The element at the intersection emits light. The EL element constructed in this way can be used as a display for characters and signs and it can also be used as an image reproducing apparatus. If the stripe pattern of the cathode 3 and anode 2 is arranged for each of red (R), green (G), and blue (B) colors, a multi-color or full-color solid flat display panel can be constructed.